A method of torque control for independent wheel drive vehicles on rough terrain

Our previous research has revealed that, for vehicles with independently driven wheels, a torque distribution based on the ratio of the vertical load of each wheel to the total vehicle load is efficient for driving on flat ground. In this research, this method of torque distribution was extended to electric off-road vehicles driving on rough ground. In order to examine the driving efficiency of these vehicles, a numerical vehicle model was constructed in the pitch plane. Simulations using the numerical vehicle model on rough ground were conducted with a proposed torque distribution and control method. The numerical results from these simulations were compared with those of a conventional vehicle to evaluate the driving efficiency and trafficability on ground with various profiles. A comparison between the simulations demonstrated that the proposed method of torque distribution to the front and rear wheels based on the ratio of the vertical load is efficient for driving on rough ground.     

Power losses and energy efficiency of multi-wheel drive vehicles: A method for evaluation

The article is concerned with assessing and providing energy and, accordingly, fuel efficiency of multi-wheel drive vehicles. It is shown that the energy efficiency depends on the distribution of power between the wheels, which, in its turn, is determined to a large extent by the driveline system and its power dividing units that are installed in the interaxle and interwheel drives of vehicles. The distribution of power between the wheels affects not only the vehicle’s slip efficiency, but also the mechanical efficiency of the driveline system as such, which should be taken into account in design. A method for assessing the energy efficiency of various vehicles involved in separate as well as combined traction and transportation work is presented.     

Analysis of torque transmitting behavior and wheel slip prevention control during regenerative braking for high speed EMU trains

The wheel-rail adhesion control for regenerative braking systems of high speed electric multiple unit trains is crucial to maintaining the stability,improving the adhesion utilization,and achieving deep energy recovery.There remain technical challenges mainly because of the nonlinear,uncertain,and varying features of wheel-rail contact conditions.This research analyzes the torque transmitting behavior during regenerative braking,and proposes a novel methodology to detect the wheel-rail adhesion stability.Then,applications to the wheel slip prevention during braking are investigated,and the optimal slip ratio control scheme is proposed,which is based on a novel optimal reference generation of the slip ratio and a robust sliding mode control.The proposed methodology achieves the optimal braking performancewithoutthewheel-railcontactinformation.Numerical simulation results for uncertain slippery rails verify the effectiveness of the proposed methodology.     

Dual variational formulation for Trefftz finite element method of elastic materials

A dual variational principle is presented for Trefftz finite element analysis. The proof of the stationary conditions of the variational functional and the theorem on the existence of extremum are provided in this paper. They are boundary displacement condition, surface traction condition and interelement continuity condition. Based on the assumed intraelement and frame fields, element stiffness matrix equation is obtained which can easily be implemented into computer programs for numerical analysis with Trefftz finite element method. Two numerical examples are considered to illustrate the effectiveness and applicability of the proposed element model.     

A theory of flexoelectricity with surface effect for elastic dielectrics

The flexoelectric effect is very strong for nanosized dielectrics. Moreover, on the nanoscale, surface effects and the electrostatic force cannot be ignored. In this paper, an electric enthalpy variational principle for nanosized dielectrics is proposed concerning with the flexoelectric effect, the surface effects and the electrostatic force. Here, the surface effects contain the effects of both surface stress and surface polarization. From this variational principle, the governing equations and the generalized electromechanical Young-Laplace equations are derived and can account for the effects of flexoelectricity, surface and the electrostatic force. Moreover, based on this variational principle, both the generalized bulk and surface electrostatic stresses can be obtained and are composed of two parts: the Maxwell stress corresponding to the polarization and strain and the remainder relating to the polarization gradient and the strain gradient. The theory developed in this paper provides the underlying framework for the analyses and computational solutions of electromechanical problems in nanodielectrics.     

Optimization of an axial coarse powder separator for low-density lignite based on the optimal seeking method

As a major equipment for thermal power plants, the main function of coarse powder separators is to separate particles into size groups according to particle diameter. With the rising coal prices, power plants are using more low-density lignite. Consequently, the original equipment does not operate under normal conditions. Therefore, to return the equipment to normal operating conditions, the isokinetic sampling method, computational fluid dynamics (CFD), and discrete phase model (DPM) based on the Euler–Lagrange method are applied in this research to analyze the effect of baffle shapes, baffle numbers, and centrifugal blades on the equipment performance index, like R₉₀. The shape of the baffle plate was optimized and improved. Preferential method was applied to determine the optimal number of baffles to ensure normal working conditions. Results show that curved baffles can suppress the axial negative gradient field below themselves better than rectangular baffles. The curved baffles selected by the optimal seeking method make full use of the negative axial gradient field and provide the particles entering the separation zone at tangential velocity in advance with the addition of centrifugal blades. Thus, pre-separation can be realized. The R₉₀ is 5 at the separator outlet and 95 at the powder return port, indicating that the output capacity of the separator returned to a reasonable operating performance.     

A numerical method for the determination of slip characteristics between the layers of a two-layer slurry flow

The observed phenomenon of slip between the layers of a flowing slurry is modelled mathematically by a finite-element-based numerical technique. This technique enables us to quantify variables such as the slip velocity and shear stress distribution at the interlayer boundary and the pressure drop within the flow domain.     

A method of calculation of the optimal lectotype for complex structures

A practical method of calculation for the optimal lectotype of complex structures is presented in this paper. On the basis of the initial structural style and designing experience, a calculating model for the optimal lectotype is established. After approximate processing of the objective functions and constraint conditions, the lectotype problem is transformed into one for solving canonical quadratic programming based on the Kuhu-Tucker condition and Lagrange multiplier. Thus the calculating process will become simpler, more reliable and accurate by introducing the weighted factor and utilizing an improved variable metric method [1].I hereby express my thanks to ray students Shuang-Bei Li, Yi-Min Song and others for their valuable help in making the calculation.     

空间拦截最优末端导引规律研究的新方法

给出了空间拦截控制的非线性微分方程，并在非线性控制系统引入了结构力学中的多重子结构法，从而求出了空间拦截非线性最优末端导引规律，同时给出了相应的数值仿真。     

A modified Hellinger-Reissner variational functional including only two independent variables for large displacement of thin shallow shell

I.IntroductionThemathematicalbasisofthefiniteelementmethodisthevariationalprinciple,andthedevelopmentofthefiniteelementmethodimpelsthevariationalprincipleitselftogetanewdevelopment.ThevariationalprincipIepresentedbyT.H.H.PianandP.Tongistheonethatthecontin…     

A simple method for the digital determination of the photoelastic fringe order

A new and simple approach to the digital determination of a photoelastic fringe order using two different loads is proposed. The relationships between the intensity values of light and the isochromatic fringe orders generated from two different loads are derived. The scheme used for the automated determination of the total fringe orders of a full-field photoelastic fringe pattern is described. The usefulness of this method is demonstrated using two isochromatic fringe patterns under two different loads. Extra filters are not needed in the proposed method as in the case of the two-wavelength method.     

A three-dimensional photographic method for measurement of phase distribution in dilute bubble flow

A three-dimensional photographic method has been developed to measure phase distributions in bubbly flow in a pipe. In this method a mirror was used to reflect a side view of the flow into the front-view direction, and then flow images in both views were taken simultaneously by one camera. After three-dimensional position and size of each bubble in the flow field were determined by matching the two bubble images in the side and front views, the phase distributions were obtained for the bubbly flow. Received: 25 April 2000 / Accepted: 21 June 2001 Published online: 29 November 2001     

A regularization-free method for the calculation of molecular weight distributions from dynamic moduli data

There are several models for the determination of molecular weight distributions (MWDs) of linear, entangled, polymer melts via rheometry. Typically, however, models require a priori knowledge of the critical molecular weight, the plateau modulus, and parameters relating relaxation time and molecular weight (e.g., k and in =kM). Also, in an effort to obtain the most general MWD or to describe certain polymer relaxation mechanisms, models often rely on the inversion of integral equations via regularization. Here, the inversion of integral equations is avoided by using a simple double-reptation model and assuming that the MWD can be described by an analytic function. Moreover, by taking advantage of dimensionless variables and explicit analytic relations, we have developed an unambiguous and virtually parameter-free methodology for the determination of MWDs via rheometry. Unimodal MWDs have been determined using only a priori knowledge of the exponent and dynamic moduli data. In addition, the uncertainty in rheological MWD determinations has been quantified, and it is shown that the reliability of the predictions is greater for the high-molecular-weight portion of the distribution.     

求解轴对称结构侧向冲击响应的一种快速算法

轴对称结构在侧向冲击载荷下的动力响应分析,一般采用解析、半解析法或者直接进行有限元数值模拟,这些方法均有一定的局限性.本文依据线性动力学问题的叠加原理,提出了一种基于有限元分析和线性叠加的快速算法.该方法首先采用多条母线对载荷进行离散,然后采用有限元计算结构在单个"载荷单元"作用下的动力响应,最后采用坐标旋转和线性叠加的方法计算得到结构在复杂分布载荷作用下的响应.算例表明,本文提出的算法是正确、有效的,并且具有快速、简便、灵活的特点.     

多重应力奇异性及其强度系数的数值分析方法

以具有两个应力奇异性次数的平面问题为例,提出了一种利用普通的数值分析结果确定奇异点附近多重应力奇异性的各阶次数以及相应的应力强度系数的数值分析方法,计算实例表明,本方法可以精确地求得各阶应力奇异性的次数,并且可以很方便地应用外插法确定出对应的应力强度系数。     

火工品可靠性的感度参数设计法

提出一种能同时满足火工品发火可靠性和安全可靠性的设计方法,把火工品可靠性指标转换成感度分布参数的取值范围,通过对感度的调节使产品满足发火可靠性和安全可靠性要求,为火工品可靠性设计提供了一条新思路。推导出了常见火工品感度在正态分布、逻辑斯谛分布、对数正态分布和对数逻辑斯谛分布等常见分布条件下把可靠性指标转换为感度分布参数的表达式,实例证明这种方法对火工品研制有指导作用。     

A new method for structural topological optimization based on the concept of independent continuous variables and smooth model

A concept of the independent-continuous topological variable is proposed to establish its corresponding smooth model of structural topological optimization. The method can overcome difficulties that are encountered in conventional models and algorithms for the optimization of the structural topology. Its application to truss topological optimization with stress and displacement constraints is satisfactory, with convergence faster than that of sectional optimizations. The project supported by State Key Laboratory of Structural Analyses of Industrial Equipment     

A structured tri-tree search method for generation of optimal unstructured finite element grids in two and three dimensions

A new method for generating finite element grids in two and three dimensions is developed. The method is based on a new search tree structure. The search tree is built upon triangles in two dimensions and tetrahedra in three dimensions. The density of elements can be varied throughout the computational domain. Efficient search algorithms for finding points in space and for finding the boundary of the domain have been developed. The speed of the grid algorithm will permit adaptive gridding during computation. The grid algorithm is generally applicable to both hydrodynamic as well as aerodynamic finite element computations. The technique has been used with success for gridding the North Sea-Skagerrak area.     

A method for analyzing on-line video images of crystallization at high-solid concentrations

Recent research has demonstrated that on-line video imaging is a very promising technique for monitoring crystallization processes. The bottleneck in applying the technique for real-time closed-loop control is considered as image analysis that needs to be robust, fast and able to handle varied image qualities due to temporal variations of operating conditions such as mixing and solid concentrations. Image analysis at high-solid concentrations turns out to be extremely challenging because crystals tend to overlap or attach to each other and the boundaries between the crystals are usually ambiguous. This paper presents an image segmentation algorithm that can effectively deal with images taken at high-solid concentrations. The method segments crystals attached to each other along the mostly related concave points on the contours of crystal blocks. The detailed procedure is introduced with application to crystallization of L-glutamic acid in a hot-stage reactor.     

不确定性参数系统振动控制闭环特征值的上、下界估计

用凸模型理论讨论参数不确定性系统的振动控制问题。把不确定系统的振动控制转化为确定性问题来处理,然后讨论不确定参数对闭环特征值的影响,提出了闭环系统特征值上、下界的计算公式。